Microsoft's free antivirus comes built-in to Windows 8 as Windows Defender, but it doesn't have an option to scan individual files by right-clicking on them. Our friends at the How-To Geek show us how to add it (or any other program) to your context menu. »2/15/13 7:30am 2/15/13 7:30am

Windows' own security tools are among the best available, but they usually require pre-installation and regular updates. If you've got to save a Windows system that's already infected—like, say, your relatives' desktop over the holidays—you can boot Windows Defender from a USB stick while you're offline. »12/21/11 4:00am 12/21/11 4:00am